The ABC understands Defence recently offered a two-year extension and a 25 per cent cost increase to the French company building the submarines, as it tries to lock in a crucial final agreement for the $50 billion project.

Manus Governor Charlie Benjamin hits out at Australia over plans to redevelop a joint naval base on the Pacific island, saying he's never been consulted on the plan that the United States is also backing.

Plans to host US warships at a redeveloped naval base on Manus Island will undermine China's plans to establish a military presence in the Pacific, says one analyst. Scott Morrison says PNG asked the US and Australia to get involved, as the countries vie for influence in the region.

It is not yet known how much US money will be pumped into the Manus base, but Vice-President Mike Pence says the Trump administration wants to "protect the sovereignty and maritime routes of Pacific Island nations".

The botched sinking of ex-HMAS Tobruk by a government contractor, which left the ship on its side and needing modifications to make it safer, will not be fixed after the risks of damaging it are deemed too high.

Japan's visiting Foreign Minister says his country would still be prepared to export its submarines to Australia if protracted contract negotiations between Defence and French company Naval Group eventually collapse.